Communication apparatus, communication method, and communication system

ABSTRACT

A physical frame is constructed, the physical frame including a medium access control super-frame payload which in turn includes a plurality of medium access control frames. With respect to the constructed physical frame, virtual carrier sense information is set in the plurality of medium access control frame so that a result of carrier sense is identical to another by virtual carrier sense based on the plurality of medium access control frames in the medium access control super-frame payload. The physical frame in which the virtual carrier sense information has been set is transmitted to a destined communication apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2004-004847, filed Jan. 9, 2004,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication apparatus, acommunication method, and a communication system for making a mediaaccess control based on carrier sense information contained in aphysical layer and carrier sense information contained in a MAC layer.

2. Description of the Related Art

A Media Access Control (MAC) is to determine how a plurality ofcommunication apparatuses making communication by sharing the same mediautilize media to transmit communication data. In the case where two ormore communication apparatuses transmit communication data by utilizingthe same media at the same time, there can occur an event (collision)that a receiving communication apparatus cannot isolate communicationdata. On the other hand, although a communication apparatus having atransmitting request exists, there can occur an event that a medium isnot utilized by any communication apparatus. In order to minimize suchevents, a media access control technique is used to control an accessfrom a communication apparatus to a medium.

However, in particular, in wireless communication, it is difficult tomonitor transmission data at the same time when a communicationapparatus transmits data. Therefore, a media access control (MAC) whichdoes not presume detection of collision is required. IEEE 802.11 whichis a typical technical standard of a wireless LAN uses a CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance). In the CSMA/CAof the IEEE 802.11, at a heater of a MAC frame, a Duration is set untila series of sequences consisting of exchange of one or more frames thatfollow the frame have terminated. In this duration, a communicationapparatus which does not relates to the sequences and which does nothave a transmission privilege determines a virtual occupancy state of amedium, thereby waiting for transmission. Therefore, an occurrence of acollision is avoided. On the other hand, a communication apparatushaving a transmission privilege using the sequences recognizes that nomedia is used to expect a duration in which a physical medium isactually occupied. The IEEE 802.11 defines that a media access iscontrolled by determining a state of a medium in accordance with acombination between a virtual carrier sense in such a MAC layer and aphysical carrier sense in a physical layer.

Up to now, the IEEE 802.11 using the CAMA/CA has promoted a highercommunication speed by mainly changing a physical layer protocol. Withrespect to a 2.4 GHz bandwidth, the IEEE 802.11 (1997, 2 Mbps) ischanged to an IEEE 802.11b (1999, 11 Mbps), and the IEEE 802.1b ischanged to an IEEE 802.11g (2003, 54 Mbps). With respect to a 5 GHzbandwidth, only an IEEE 802.11a (1999, 54 Mbps) is now provided asstandard. In order to define a standard for a higher processing speed inboth of the 2.4 GHz bandwidth and the 5 GHz bandwidth, an IEEE 802.11TGn (Task Group n) has already been established.

If a frequency spectrum identical to that in the existing standard isused in achievement of a higher communication speed, a communicationapparatus newly provided enables coexistence with a communicationapparatus that follows the existing standard. It is preferable thatbackward compatibility be maintained. Therefore, it is considered to bebasically good that a protocol of a MAC layer follows the CSMA/CA whichmatches the existing standard. In this case, it is necessary to ensurethat a time-related parameter associated with the existing standard, forexample, an interframe time interval (IPS: Interframe Space) or aback-off duration conforms to the existing standard.

Here, even if a higher data rate has been successfully achieved withrespect to a physical layer, there is a problem that a substantialcommunication throughput cannot be improved. That is, in the case wherea higher data rate of the physical layer has been achieved, a format ofa PHY frame is no longer effective. It is considered that an overheadcaused by this problem inhibits improvement of throughput. In the PHYframe, a time-related parameter according to the CSMA/CA is fixedlyassociated with the MAC frame. In addition, a PHY frame header isrequired for each MAC frame.

One method for reducing an overhead to improve a throughput includesBlock ACK introduced in the latest draft IEEE 802.11e draft 5.0(strengthening QoS of the IEEE 802.11). By using this method, aplurality of MAC frames can be continuously transmitted withoutback-off. Thus, an amount of back-off can be reduced, but a header of aphysical layer cannot be reduced. In addition, according to anaggregation introduced in accordance with an earlier draft IEEE 802.11e,both an amount of back-off and a physical layer header can be reduced.However, a length of a frame of a physical layer including the MAC framecannot be set to about 4 Kbytes or more because of a restriction on aconventional physical layer. Therefore, large restriction applies toimprovement of efficiency. Even if a frame of a physical layer can beincreased in length, there occurs a problem that error tolerance islowered.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to provide a communication apparatus,a communication method, and a communication system which enablecoexistence of an existing apparatus, and which can eliminate anoverhead due to transmission of a plurality of frames by efficient useof a frame format and can improve a substantial communicationthroughput.

A communication apparatus according to an aspect of the presentinvention comprises: a physical frame construction device configured toconstruct a physical frame having a medium access super-frame payloadwhich includes a plurality of medium access control frames; a firstsetting device configured, with respect to the physical frameconstructed by the physical frame construction device, to set virtualcarrier sense information in the plurality of medium access controlframes so that a result of the carrier sense is identical to anothereven by a virtual carrier sense based on the plurality of medium accesscontrol frames in the medium access control super-frame payload; and atransmission device configured to transmit a physical frame in whichvirtual carrier sense information has been set by the first settingdevice to a destined communication apparatus.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a block diagram depicting a configuration of a communicationapparatus according to a first embodiment of the present invention;

FIG. 2 is a view showing an example of a frame format for use in acommunication apparatus according to an embodiment of the presentinvention;

FIG. 3 is a view showing an example of a format of a PHY frame of afirst type;

FIG. 4 is a view showing an example of a format of a PHY frame of asecond type;

FIG. 5 is a view showing an example of a format of a MAC frame;

FIG. 6 is a view showing an example of a communication system accordingto one embodiment of the present invention;

FIG. 7 is a view showing an example of a carrier sense state of eachcommunication apparatus in the case where a value of a duration fieldhas been defined in accordance with a method 1;

FIG. 8 is a view showing an example of a carrier sense state of eachcommunication apparatus in the case where a value of a duration fieldhas been defined in accordance with a method 2;

FIG. 9 is a view showing an example of a format of a partial ACK frame;

FIG. 10 is a view illustrating a power saving control according to asecond embodiment of the present invention;

FIG. 11 is a view showing a transmission managing table for use inretransmission control according to a third embodiment of the presentinvention;

FIG. 12 is a view showing a main queue and a subsidiary queue for use inretransmission control of a transmitting communication apparatus;

FIG. 13 is a flowchart showing operating procedures for retransmissioncontrol of the transmitting communication apparatus;

FIG. 14 is a view showing a subsidiary queue for use in a receivingcommunication apparatus;

FIG. 15 is a flowchart showing operating procedures of the receivingcommunication apparatus;

FIG. 16 is a view showing an example of a frame format for use in acommunication apparatus according to a fourth embodiment of the presentinvention;

FIG. 17 is a view showing an example of a carrier sense state of eachcommunication apparatus in the case where a value of a duration field isdefined in the communication apparatus according to the fourthembodiment;

FIG. 18 is a view showing an example of a super-frame header format foruse in a communication apparatus according to a fifth embodiment of thepreset invention;

FIG. 19 is a view showing an example of a frame format for use in acommunication apparatus according to a sixth embodiment of the presetinvention; and

FIG. 20 is a view showing an example of a frame format for use in acommunication apparatus according to a seventh embodiment of the presetinvention.

DETAILED DESCRIPTION OF THE INVENTION FIRST EMBODIMENT

FIG. 1 is a block diagram depicting a configuration of a communicationapparatus according to a first embodiment of the present invention. Thiscommunication apparatus 100 is provided as an apparatus whichcommunicates with another communication apparatus via a wireless link.This communication apparatus includes processing units 101, 102, 103which correspond to a physical layer, a MAC layer, and a link layer,respectively. These processing units are implemented as an analog ordigital electronic circuit according to packaging or as a firmwareexecuted by a CPU incorporated in an LSI. An antenna 104 is connected tothe processing unit 110 of a physical layer (hereinafter, an expressionof “processing unit” is omitted). The MAC layer 102 includes anaggregation (integration) processing portion 105 according toembodiments of the present invention. The aggregation processing portion105 comprises at least a carrier sense control portion 106 in the firstembodiment. A retransmission control portion 107 shown in the figurerelates to a second embodiment of the present invention, and a powersaving control portion 108 relates to a third embodiment of the presentinvention. These elements will be described in detail in theembodiments. A physical layer 101 is composed so as to be compatiblewith physical layer protocols of two types. For the purpose of eachprotocol process, the physical layer 101 has a first type physical layerprotocol processing portion 109 and a second type physical layerprotocol processing portion 110. In packaging, a circuit is often sharedbetween the first type physical layer protocol processing portion 109and the second type physical layer protocol processing portion 110.Thus, these portions do not always exist independently.

In the embodiments of the present invention, it is assumed that a firsttype physical layer protocol is provided as a protocol defined inaccordance with an IEEE 802.11a, and that a second type physical layerprotocol is provided as a protocol with a so-called MIMO (Multiple InputMultiple Output), using a plurality of antennas at a transmitting sideand a receiving side, respectively. Even frequency bandwidths aremaintained to be identical to each other, it is possible to expect anincrease of a transmission capacity which is substantially parallel tothe number of antennas. Thus, the MIMO is one of the techniques whichcan be utilized for the achievement of a higher throughput. With respectto the link layer 103, it has a normal link layer function defined inaccordance with the IEEE 802. A technique used to improve a transmissionrate is not limited to the MIMO. For example, a method for increasing afrequency occupying bandwidth and a combination of such increasingmethod and the MIMO may be used.

FIG. 2 is a view showing an example of a frame forma for use in acommunication apparatus according to an embodiment of the presentinvention. A frame format 200 schematically shows a frame structureaccording to a physical layer and a MAC layer. Specifically, it isassumed that the frame format follows the IEEE 802.11 or its extension.The frames in accordance with the IEEE 802.11 are roughly divided intothree types, i.e., a control frame, a management frame, and a dataframe. Although it is assumed that the embodiment of the presentinvention is mainly applied to the data frame, it does not always implythat application to the control frame or management frame is omitted. Asshown in FIG. 2, the frame format 200 includes a PHY header 201; a MACsuper-frame header 202 and a MAC super-frame payload 203; and a PHYtrailer 204. The MAC super-frame header 202 and the MAC super-framepayload 203 each correspond to a PHY payload described later.

The PHY header 201 is processed by the physical layer 101 of a receivingcommunication apparatus. That is, the physical layer 101 carries outdetection of a frame head; carrier sensing, establishment of timingsynchronization, amplitude control of an amplifier (AGC: Automatic GainControl), keeping track of a transmitting carrier frequency (AutomaticFrequency Control), estimation of a transmission channel and the like,based on the received PHY header 201. In addition, the physical layer101 carries out detection of a modulation scheme or encoding rate, and atransmission rate and data length of the PHY payload that follows thePHY header 201.

FIG. 3 is a view showing an example of a format of a first type PHYframe. This format is identical to that defined in accordance with theIEEE 802.11a. The first type PHY frame is used when a communicationapparatus according to embodiments of the present invention communicateswith an existing communication apparatus. This PHY frame is processed bythe first type physical layer protocol processing portion 109 of thephysical layer 101 (hereinafter, referred to as communication conformingto the IEEE 802.11a). As shown in FIG. 3, a first PHY frame, i.e., afirst type PLCP frame includes a PLCP (Physical Layer ConvergenceProtocol) short preamble 301 and a PLCP long preamble 302; a signalfield 303; and a data field 304. The signal field 303 corresponds to aPLCP header 305. As shown in the figure, this signal field includes atransmission rate field 306 and a data length field 307. Of course, thefirst type PHY frame is not limited to that defined in accordance withthe IEEE 802.11a.

FIG. 4 is a view showing an example of a format of a second type PHYformat. The second type PHY frame, i.e., a second type PLCP frameincludes a first header portion 401 for a first physical layer protocol;and a second header portion 402 for a second physical layer protocol.The first header portion 401 and the second header portion 402 areallocated along a time series, each of which corresponds to the PHYheader 201 shown in FIG. 2. In addition, the second type PHY frameincludes a PHY payload 403 that follows the second header portion 402;and Tail and Pad bits 404. The PHY payload 403 corresponds to the MACsuper-frame header 202 and the MAC super-frame payload 203 in FIG. 2,and corresponds to a PSDU (PLCP Service Data Unit) in a format of aphysical layer. Further, the Tail and Pad bits 404 correspond to the PHYtrailer 204 of FIG. 2.

The first header portion 401 for the first type physical layer protocolincludes a PLCP short preamble 405; a PLCP long preamble 406; and asignal field 407. The signal field 407 corresponds to all or part of thePLCP header. An effective value is set so as to carry out physicalcarrier sensing in at least a transmission rate field 408 and a datalength field 409. Such a signal field 407 has the same informationcontents and modulation scheme which correspond to those of the PLCPheader 305 of the first type PHY frame shown in FIG. 3.

The second header portion 402 for the second type physical layerprotocol includes a MIMO PLCP long preamble 410; a MIMO signal field411; and a MIMO service field 412. The exemplary format shown in FIG. 4is for the purpose of explanation, and may be changed if necessary. InFIG. 4, for example, MIMO PLCP long preamble 410 and MIMO signal field411 can be swapped in their arrangement order. The MIMO signal field 411includes a transmission rate field 413 and a data length field 414 asshown in the figure, and is referenced in physical carrier sensing. TheMIMO PLCP long preamble 410 is used when a receiving communicationapparatus of the MIMO capable of interpreting the second type physicallayer protocol acquires transmission channel information required for adecoding process.

By defining the second type PHY frame as a format as shown in FIG. 4, anexisting communication apparatus which can be operated in accordancewith only the first type physical layer protocol can interpret at leasta first signal field 407. Thus, carrier sensing of the physical layercan be correctly carried out in accordance with the signal field 407.Therefore, the same carrier sense information at physical layer can beshared between such an existing communication apparatus and the firsttype and second type physical layer protocols each. The existingcommunication apparatus can not share the carrier sense informationcontained in the MAC layer. However, this fact does not cause a problembecause of a partial ACK described later.

When a PHY payload is transmitted on a physical medium, informationrepresenting a medium occupation duration (hereinafter, referred to as a“physical occupation duration”) due to the PHY payload is utilized ascarrier sense information contained in a physical layer together withsignal intensity. At a time point when a receiving communicationrecognizes a physical occupation duration of the PHY payload by means ofphysical carrier sensing, the communication apparatus interprets that aphysical medium is occupied (PHY busy) during the duration. In addition,this communication apparatus interprets that the physical medium isoccupied also in a duration in which signal intensity exceeds apredetermined threshold value. The physical occupation duration of thePHY payload can be obtained by means of calculation based on atransmission rate (408 or 413) of the PHY payload and data length (409or 414) detected in the receiving communication apparatus. Specifically,this duration can be obtained by dividing a value of a data length fieldexpressed in an octet length by a value of a transmission rate field.This also applies to a first type PHY frame shown in FIG. 3.

In the case where a maximum data length (4096 octets in the IEEE802.11a) of the PHY payload which the first type physical layer protocolpermits is actually shorter than a maximum data length of the PHYpayload which the second type physical layer protocol permits, thecarrier sense information contained in the physical layer can be sharedby intentionally falsely setting the transmission rate field 408 and thedata length field 409 so that the physical occupation duration of thePHY payload becomes proper.

Here, a description will be given again with reference to FIG. 2. OneMAC super-frame, which includes a plurality of MAC frames, correspondsto a single PHY frame. In the frame format 200 shown in the figure, theMAC super-frame header 202 always has data length fields 1 to 8 of eightMAC frames. Although the MAC super-frame header 202 has a fixed lengthin the present embodiment, the MAC super-frame header 202 may have avariable length by adding information indicating the number of MACframes.

In the case where, as shown in FIG. 2, only four MAC frames 1 to 4 areincluded in the MAC super-frame payload 203, the MAC frame data lengthfields 5 to 8 corresponding to the MAC frames 5 to 8 which do not existin the same payload 203 are padded with zero values. In addition, duringretransmission control described later, for example, in the case whereMAC frame 1 and MAC frame 3 are required to be retransmitted while MACframe 2 and MAC frame 4 are not required to be retransmitted, the MACframe data lengths are specified such as MAC frame data length 1>0, MACframe data length 2=0, MAC frame data length 3>0, and MAC frame datalength 4=0. I.e., the MAC frame data lengths corresponding to the MACframes which are not subject to retransmission are set to zero.

An HCS 205 denotes a Header Check Sequence. In order to enable detectionof an error of the MAC super-frame header 202, the sequence is added tothe same header 202. In the case where the receiving communicationapparatus has detected an error of the MAC super-frame header 202 bymeans of the NCS 205, it is interpreted that all the MAC frames includedin the MAC super-frame payload 203 are destroyed. It is preferable thatthe number of MAC frames included in the MAC super-frame payload 203 bedynamically restricted in order to prevent a buffer overflow in thereceiving communication apparatus. For this purpose, for example,Sliding Window control described later can be utilized.

FIG. 5 is a view showing an example of a format of a MAC frame. One MACframe included in the MAC super-frame payload 203 of FIG. 2 includes aMAC header 500; a frame body 501; and an FCS (frame check sequence) 502.The MAC header 500 includes a frame control field 503; a Duration field504; address fields 505 to 507 and 509; and a sequence control field508. The frame body 501 has a variable length in the range of 0 to 2312octet lengths, and is provided as a payload of a MAC frame whichcorresponds to a MPD (MAC Protocol Data Unit).

With a higher communication data rate of a physical layer in accordancewith a second type physical layer protocol (MIMO is defined in thepresent embodiment), a plurality of MAC frames are included in a PHYframe as a MAC super-frame (an aggregation), thereby efficientlyconfiguring a format in the present embodiment. While an overhead foreach PHY frame, i.e., a PLCP header, a variety of IFSs (Inter FrameSpace), back-off and the like, is the same, the carried data in a PHYframe is increased by the aggregation. Thus, a communication throughputcan be improved substantially.

A media access control is made based on carrier sensing of a physicallayer and carrier sensing of a MAC layer. Now, a description will begiven with respect to a robust MAC carrier sensing according to afeature of the first embodiment.

FIG. 6 is a view showing an example of a communication system accordingto one embodiment of the present embodiment. In this communicationsystem, it is assumed that communication apparatuses 1 to 4 makecommunication via a wireless link. The communication apparatuses 1 to 3shown in the figure each have a feature shown in FIG. 1. In contrast,the communication apparatus 4 comprises only the first type physicallayer protocol processing portion 109, and does not comprise the secondtype physical layer protocol processing portion 110. Therefore, thiscommunication apparatus corresponds to an existing communicationterminal which does not carry out transmission of a MAC super-frame.Hereinafter, a description will be given assuming that communication ismade while the communication apparatus 1 is defined as a transmittingside and the communication apparatus 2 is defined as a receiving side,and assuming that the communication apparatus 3 and communicationapparatus 4 do not relate to this communication.

As has been described with reference to FIGS. 2 and 5, each of the Macframes included in the MAC super-frame (aggregation) payload 203includes: a MAC header 500; and an FCS 502 capable of detecting an errorof the entire MAC frame which includes the MAC header 500. Thetransmitting communication apparatus 1 sets a value of a duration field504 of each MAC header 500 in each Mac frame as follows whenconstructing the MAC super-frame payload 203 to be transmitted. That is,when at least one MAC frame included in the MAC super-frame payload 203is correctly received, communication apparatus 2 having received theframe sets a value such that a carrier sense state of a MAC layer can becorrectly recognized. Specifically, for example, either of the method 1and method 2 described below are followed.

(Method 1): A value of a duration starting with a time point when a PHYframe including the MAC super-frame 203 has terminated and ending with atime point when a MAC frame defined as a continuous sequence in a MAClayer has been exchanged, or alternatively, a value of a duration endingwith a time point when a medium reservation carried out in the MAC layerhas terminated, are set in the duration field 504. According to themethod 1, the same value is set in the duration fields 504 of at least aplurality of MAC frames included in the MAC super-frame 203 (refer toFIG. 7).

(Method 2): A value of a duration starting with a time point when theMAC frame including a duration field has terminated and ending with atime point when a MAC frame defined as a continuous sequence in a MAClayer has been exchanged, or alternatively, a value of a duration endingwith a time point when a medium reservation carried out in the MAC layerhas completed, is set in the duration field 504. According to the method2, different values each are set in the duration field 504 of the MACframe included in the MAC super-frame 203 (refer to FIG. 8).

Further, a receiver address is set as follows in one of the addressfields 505 to 507 and 508 contained in the MAC header 500 in each MACframe (specifically, corresponding to address 1 to address 3 and address4). That is, the MAC address of the corresponding communicationapparatus is set so that all the MAC frames with the duration valuespecified above in the same MAC super-frame each indicate the samereceiver.

In the present embodiment, the communication apparatus 2 having a MACaddress which corresponds to a receiver address generally relates to aMAC frame exchange sequence in a duration specified in the durationfield 504, and has a transmission privilege that follows a rule on theMAC frame exchange sequence. In contrast, the communication apparatuses3, 4 which do not correspond to the receiver address do not relate theMAC frame exchange sequence, and does not have the transmissionprivilege in this duration.

The communication apparatus 3 which does not relate to the MAC frameexchange sequence refers to a value of the duration field 504 in the MACheader 500 of any of the received MAC frames with the duration valuespecified above; interprets that a medium is virtually (logically)occupied in a duration which corresponds to this value; and does notcarry out frame transmission until the duration has terminated. Such aduration is referred to as a “virtual medium occupation duration”. Thus,the communication apparatus 3 sets a NAV (Network Allocation Vector) fordisabling transmission in the virtual medium occupation duration. SuchNAV setting based on the virtual carrier sensing of the MAC layer isprovided regardless of a physical medium occupation duration based oncarrier sensing of a physical layer. On the other hand, like thecommunication apparatus 3, the existing communication apparatus 4 whichdoes not relate to the MAC frame exchange sequence enters a state ofwaiting for an EIFS (Extended IFS) duration. An operation of theexisting communication apparatus 4 in this case will be described laterin detail

In the embodiments of the present invention, since a plurality of MACframes are integrated into one PHY frame, carrier sensing of the MAClayer is robustly carried out, whereby a virtual medium occupationduration can be properly set.

FIG. 7 shows an example of a carrier sense state of each communicationapparatus in the case where a value of the duration field 504 has beendefined in accordance with the above method 1. A value of the durationfield 504 of MAC frame 1, MAC frame 2, MAC frame 3, and MAC frame 4 eachis set to a sum of a SIFS (Short IFS) and a transmission time of apartial ACK, one example of which is shown in FIG. 9.

It is necessary to define a rule so that the transmitting communicationapparatus 1 can calculate a transmission time of the partial ACK and sothat a receiving side can uniquely select a method of transmitting thepartial ACK. It is assumed that the partial ACK is carried by a PHYframe conforming to the IEEE 802.11a which is the first type physicalprotocol shown in FIG. 3, and is transmitted at a maximum mandatorytransmission rate conforming to the IEEE 802.11a. As described later, itis important that the partial ACK can be decoded and interpreted by acommunication apparatus capable of interpreting only the first typephysical protocol to ensure the purpose of backward compatibility.

When the receiving communication apparatus 2 receives a frametransmitted from the transmitting communication apparatus 1, thereceiving communication apparatus 2 first recognizes that a medium isbusy, i.e., enters a occupying state by carrier sensing of the physicallayer. Further, the communication apparatus 3 (capable of interpretingfirst type and second type physical protocols and its address isdifferent from the receiver address and a transmitter address specifiedin MAC frame 1 to MAC frame 4) and the communication apparatus 4(capable of interpreting only the first physical protocol) recognizethat a medium enters an occupying state by carrier sensing of thephysical layer similarly.

Next, if it is determined that any of MAC frame 1 to MAC frame 4 iscorrect by the FCC, the receiving communication apparatus 2 recognizesthat there is no need for setting NAV because the destination address isidentical to an address of the communication apparatus 2. In accordancewith a rule on the MAC frame exchange sequence, the receivingcommunication apparatus 2 transmits the partial ACK after an elapse ofthe SIFS after the receiving of the second type PHY frame including theMAC super-frame has completed.

If it is determined that any of MAC frame 1 to MAC frame 4 is correct bythe FCS, the communication apparatus 3 recognizes that NAV should be setas a receiver address is different from the address of the communicationapparatus 3. The communication apparatus 3 sets NAV in a duration whichcorresponds to a value of the duration field 504 included in any of MACframe 1 to MAC frame 4 determined to be correct by the FCS.

The existing communication apparatus 4, which cannot recognize a signalfield and subsequent of a second type PHY frame, advances processing asif it were a first type PHY frame. Then, this communication apparatuscalculates an FCS and detects an error at the end of the frame.Alternatively, the communication apparatus detects an error at the endof the frame, since it recognize that there occurs a PHY fame of suchtype which cannot be interpreted. In these cases, the communicationapparatus 4 cannot recognize correctly a virtual carrier sense state ofthe MAC layer to be set by reception of the PHY frame, and thus, entersan error recovery state. Namely, this communication apparatus enters astate of waiting for an EIFS duration which is the longest IFS. In thiswaiting state, the communication apparatus 4 receives a partial ACKoriginated from the receiving communication apparatus 2 beforeterminating the EIFS. As described above, since a partial ACK istransmitted at a mandatory rate conforming to the IEEE 802.11a which isthe first type physical layer protocol, the existing communicationapparatus 4 can interpret this ACK. If the partial ACK is correctlyreceived, carrier sensing of the MAC layer is correctly carried out.Thus, the waiting state caused by the EIFS is cancelled, and no problemoccurs. Therefore, the communication apparatus according to embodimentsof the present invention and the existing (legacy) communicationapparatus can coexist.

The transmitting communication apparatus 1, the communication apparatus3, and the existing communication apparatus 4 each receive the partialACK transmitted by the receiving communication apparatus 2. A value ofthe duration field 504 in this partial ACK is set to 0, andconcurrently, each of the communication apparatuses sets NAV to 0. A MACframe exchange sequence that follows the partial ACK may be defined onthe MAC sequence. In that case, the value of the duration field 504 inthe partial ACK is obtained as a value indicating an end time point ofthe MAC sequence.

If all the communication apparatuses have data to be transmitted, theycontinuously enter a waiting state caused by the DIFS (DCF IFS, i.e.,Distributed Coordinate Function IFS). In this DIFS duration, if carriersensing of the physical layer and MAC layer indicates an idle state, acurrent state enters a back-off duration, and countdown is started.Then, a communication apparatus in which a counter initialized by randomnumbers has reaches 0 first in the apparatuses obtains a transmissionprivilege.

Now, an error which can occur during receiving of the second type PHYframe will be described here. Consider a case in which there is no MACframe which is determined to be correct by the FCS as a result of thecommunication apparatus 2 decoding the MAC frames included in the secondtype PHY frame. In the case where there is no MAC frame which isdetermined to be correct by the FCS, the communication apparatus 2cannot recognize correctly a virtual carrier sense state of a MAC layerto be set based on receiving of the second type PHY frame, and thus, acurrent state goes to an error recovery state. Namely, the current stategoes to a state of waiting for an EIFS duration which is the longestIFS. In the case where the non-receiving communication apparatus 3 goesto the state of waiting for the EIFS duration and the communicationapparatus 2 receives at least one MPDU correctly, the communicationapparatus 3 receives the partial ACK transmitted from the receivingcommunication apparatus 2. If the partial ACK is correctly received bythe communication apparatus 3, carrier sensing of the MAC layer iscorrectly carried out as described later, and therefore, the waitingstate of the communication apparatus 3 caused by the EIFS is canceled atthis time.

Assuming that an error occurs at the communication apparatus 2 and thecommunication apparatus 2 simultaneously during receiving as describedabove, the receiving communication apparatus 2 goes to the state ofwaiting for the EIFS duration without sending the partial ACK. The EIFSstate at the communication apparatus 3 is not reset by the Partial Acksent from the communication apparatus 2. In this case, in the case wherethe EIFS duration is longer than a duration caused by NAV and DIFS, astate in which any communication apparatus cannot carry out transmissionoccurs at least in this duration. This event reduces use efficiency of aphysical medium for use in communication, and thus, should be avoidedwith an utmost effort.

However, according to the embodiments of the invention, since aplurality of MAC frames are included in the MAC super-frame payload 203,carrier sense information contained in the MAC layer can be obtainedbased on any of the plurality of MAC frames. As a result, an error isless likely to occur during receiving as described above. Specifically,a plurality of MAC frames from among the MAC frames included in the MACsuper-frame have information required for carrier sensing of the MAClayer, i.e., carrier sense information contained in the MAC layer whichincludes at least the duration field 504 and a receiver address. Sinceeach of these MAC frames has an FCS, the presence or absence of an errorcan be detected. Even if an error occurs during receiving of any MACframe, at least one of the remaining MAC frames may be correctlyreceived. Therefore, carrier sensing of the MAC layer can be robustlycarried out based on at least one MAC frame which has been successfullyreceived, and an error tolerance can be relatively enhanced duringreceiving per PHY frame.

FIG. 8 shows an example of a carrier sense state of each communicationapparatus in the case where a value of the duration field 504 has beendefined in accordance with the above method 2. Only a difference fromFIG. 7 will be briefly described here. The value of the duration field504 of MAC frame 1 is set at a value of a sum among a transmission timeof MAC frame 2, MAC frame 3, and MAC frame 4, a SIFS duration, and atransmission time of a partial ACK frame. The value of the durationfield 504 of MAC frame 2 is set at a value of a sum among a transmissiontime of MAC frame 3 and MAC frame 4, a SIFS duration, and a transmissiontime of a partial ACK frame. A value of each duration field 504 of MACframe 3 and MAC frame 4 is also set in a similar method. Namely, unlikethe case of FIG. 7, the values of the duration field 504 are differentfrom each other depending on each MAC frame, and concurrently, thesettings of NAV are also different from each other.

With respect to NAV set by the communication apparatus 3 (whose addressis different from the receiver address and the transmission sourceaddress of each of MAC fame 1 to MAC frame 4 and which can interpretfirst type and second type physical protocols), an end time point of aMAC frame including the duration field 504 is defined as a start point,and the NAV value is set.

In such a method 2 as well as method 1, a medium occupation time i.e.NAV set by each of the MPDU in the MAC super-frame terminates at thesame time as is evident from FIG. 8.

SECOND EMBODIMENT

A second embodiment of the present invention relates to power savingcontrol. FIG. 10 is a view illustrating power saving control accordingto the second embodiment of the invention. According to the presentembodiment, the transmitting communication apparatus 1 and the receivingcommunication apparatus 2 being in communication are controlled so asnot to be switched to a power saving state, and a communicationapparatus which does not relate to communication can be controlled so asto be switched to the power saving state.

At a time point when the communication apparatus 3 recognizes any of theMAC frames included in the MAC super-frame included in the second typePHY frame is recognized to be correct by the FCS, the communicationapparatus 3 recognizes that there is no need for carrying out receptionor transmission over a duration in which NAV set by the communicationapparatus 3 itself terminates, and starts a power saving operation fromthat time point. However, in this case, each MAC frame must be encodedin the PHY frame so that such each MAC frame is decoded in a time serieson the receiving side.

A power saving state terminates at a NAV end time point because there isa need for carrying out carrier sensing in the DIFS duration andback-off duration after terminating NAV. By recognizing the power savingstate, power saving can be achieved by stopping an unnecessary circuit.Specifically which circuit is stopped at which timing or is restarted atwhich timing depends on implementation.

With respect to the existing communication apparatus 4 as well, at atime point when a continuation time of a second type PHY frame isrecognized based on a signal 407 in a second type PHY frame and it isrecognized that this PHY frame is transmitted in a scheme in which thecommunication apparatus 4 cannot carry out decoding, a duration for thePHY frame to terminate can be recognized as a power saving state.However, during the EIFS duration, there is a need for carrying outcarrier sensing, and the power saving state is not established.

THIRD EMBODIMENT

A third embodiment of the present invention relates to retransmissioncontrol. From the viewpoint of communication fairness or QoS (Quality OfService), it is preferable that retransmission be controlled to limitconsecutive communication to the same terminal. FIG. 11 is a viewshowing a transmission managing table for use in retransmission controlaccording to the third embodiment of the invention. In this transmissionmanaging table, a Sliding Window is expressed. For convenience ofexplanation, the transmission managing table expresses a full history oftransmission and reception including retransmission. However, in actualimplementation of a communication apparatus, there is no need forstoring the full history described here.

Consider a state in which the same transmitting communication apparatuscontinuously transmits a MAC frame (MPDU) to the same receivingcommunication apparatus prior to communication of another frame. Inorder to avoid biases assignment of transmission and receptionprivileges to specific communication apparatuses or a pair of atransmitting communication apparatus and a receiving communicationapparatus, the number of MAC frames which can be continuouslytransmitted is limited based on the transmission managing table. Thislimitation is effective until either of the transmitting communicationapparatus and the receiving communication apparatus has been changed.

In the transmission managing table shown in FIG. 11, a limited number ofMAC frames which can be continuously transmitted is defined to a maximumof 16, and this is referred to as full window W_all. In addition, to aseries of MAC frames (MPDU) targeted to be continuously transmitted, asequence number (Seq. No.) is assigned in the transmission managingtable. A start point of full window W_all corresponds to SEQ1, and itsend point corresponds to SEQ16. Transmission (or retransmission) offrames included in full window W_all is delimited, and is carried outbased on a series of transmission sequences (or retransmissionsequences) described later. Full window W_all may be variable inconsideration of a state of congestion, priority assigned to thereceiving communication apparatus and the like. If full window W_all isincreased, although a delay and a jitter increase or unfairness betweenthe communication apparatuses or the like increases, a whole throughputis likely to be improved. Therefore, when it is recognized that realtime communication of voice or mobile image exists, dynamic control maybe made such that the size of the full window is reduced. In such acontrol, the whole throughput itself is likely to be reduced, and thus,dynamic control may be used in combination with any traffic control suchas priority control based on traffic type.

In addition, a maximum value of full window W_all and window W_n (n=1,2, 3, . . . ) at each time point may be set after negotiation is carriedout in accordance with any protocol for each pair of transmitting andreceiving communication apparatuses or a common value in the wholesystem may be used. Even in the case where the system common value isused, there is no need for setting a fixed value.

A retransmission control portion 107 of the transmitting communicationapparatus constructs a MAC super-frame with reference to thetransmission managing table. At this time, the retransmission controlportion 107 selects a MAC frame to be included in the MAC super-frame inconsideration of the necessity of retransmission.

Although a plurality of MAC frames are included in a single MACsuper-frame, a maximum number of MAC frames which can be stored islimited. In the present embodiment, up to eight MAC frames can beincluded. The receiving communication apparatus needs to be able tobuffer the above maximum number of MAC frames. The receivingcommunication apparatus passes a MAC frame, in the form that a sequenceis kept, to the upper layer of the MAC layer. In this manner, thecorrectly received MAC frame needs to be stored in a buffer until it hasbeen determined that a MAC frame having a sequence number preceding thatof the correctly received MAC frame is correctly received byretransmission or that a MAC frame having a sequence number precedingthat of the correctly received MAC frame is not to be retransmitted anymore (e.g. by timeout). This buffer has a space to store MAC frames froma MAC frame with the lowest sequence number which is yet to be receivedcorrectly to a MAC frame with a sequence number which corresponds to thelowest sequence number +7.

In FIG. 11, the range of these sequence numbers at each time point isexpressed as a start point and an end point by windows W1 to W5,respectively. The MAC frame to be included in the MAC super-frame andtransmitted by the transmitting communication apparatus is limited toMAC frames required to be transmitted because they are not acknowledgedand need to be retransmitted in this window range as well as MAC framesnewly transmitted in this window range. In FIG. 11, in the case where“LenX” is written in each of TX1 to TX5, a MAC frame of sequence numberX is transmitted by transmission of the corresponding MAC super-frame.In the case where “0” is written, the MAC frame of the correspondingsequence number is not transmitted. These values correspond to datalength fields 1 to 8 of the MAC frames in the MAC super-frame header 202shown in FIG. 2. In the case where “o” is entered in each of RX1 to RX5,this indicates that the MAC frame of the corresponding sequence numberhas already been correctly received. In the case where “x” is entered ineach of RX1 to RX5, this indicates that the MAC frame of thecorresponding sequence number has never been correctly received untilthis time point has been reached. These “o” and “x” correspond to trueand false values, and correspond to values of a partial ACK bit map(Partial ACK Bitmap) 91 in the partial ACK frame shown in FIG. 9.

At the beginning of windows W1 to W5 at each time point, the sequencenumber of a MAC frame which has never been correctly received by thereceiving communication apparatus is entered. The lower limit of anadvancing speed at the start point of this window is determined by theretransmission count. After the predetermined retransmission count hasbeen reached, the windows must be advanced beyond a window size (8 inthis case). If this condition has not been met, the transmittingcommunication apparatus terminates (re)transmission. In short, acondition in which transmission of continuous MAC frames is continued isthat the MAC frame is received on the receiving side within theretransmission limit.

In the present embodiment, assuming that the retransmission limit is 3,it is determined that retransmission has failed, although the MAC frameof sequence number 15 has been retransmitted three times from TX3 toTX5, in an example shown in FIG. 11. Therefore, a series ofretransmission sequences to a communication apparatus being aretransmission destination is canceled at this time point. Such aretransmission limit is effective in that, for example, in the casewhere the receiving communication apparatus comes out of the radiocommunication coverage, wasteful transmission can be avoided accordingto, for example, a state in which a transmission channel state with thereceiving communication apparatus is worsened over a comparatively longperiod of time.

Only the transmitting communication apparatus recognizes thatretransmission sequences have terminated at this time point. Thereceiving communication apparatus passes sequence numbers 1 to 14 from abuffer to a host unit. However, sequence number 15 is not correctlyreceived, and thus, sequence number 16 is left in the buffer. In thiscase, the receiving communication apparatus receives a MAC super-framestarting with a MAC frame having a sequence number which is greater thana sequence number of a MAC frame which has not been acknowledged byone's own device. In this manner, the receiving communication apparatusrecognizes that the transmitting communication apparatus has given upretransmission of the MAC frame which has not been acknowledged by one'sown device. Then, the receiving communication apparatus passes to theupper layer processing step all of the MAC frames each having a sequencenumber which is smaller than the first sequence number of the new MACsuper-frame, and empties the buffer. In a single MAC super-frame,sequence numbers are continuously assigned to MAC frames each. Thus,even if the first MAC frame is destroyed, if there exist one or moreother MAC frames which have been normally received successfully, thereceiving communication apparatus can recognize the sequence number ofthe first MAC frame.

If there does not exist receiving of a new MAC super-frame from thetransmitting communication apparatus over a predetermined period oftime, the receiving communication apparatus passes to the upper layerprocessing step the MAC frame retained in the buffer assigned to thetransmitting communication apparatus.

Now, a description will be given with respect to an operation of each ofthe transmitting communication apparatus and the receiving communicationapparatus when retransmission control is made based on the transmissionmanaging table described above. In the following description, atransmitting communication apparatus is defined as STA0, and a receivingcommunication apparatus is defined as STA1.

FIG. 12 is a view showing an example of a main queue 121 and asubsidiary queue 122 for use in retransmission control of thetransmitting communication apparatus in accordance with the presentembodiment. The subsidiary queue 122 corresponds to the buffer describedwith reference to FIG. 11.

FIG. 13 is an example of a flowchart showing operating procedures forretransmission control of the transmitting communication apparatus inaccordance with the embodiment. First, a MAC frame to be (re)transmittedis selected (step S1). In this step S1, from the main queue 121 storingthe MAC frames specified with receiver addresses (STA1 to STA4 in thiscase) of a variety of communication apparatuses, the MAC frame in whichthe communication apparatus (STA1 in this case) of the transmissiondestination to be (re)transmitted in accordance with a series of thesequences is selected in a range that does not exceed full window(W_all) and the window range (W1, for example) at that time. Then, theselected MAC frames are extracted in the subsidiary queue 122 having thesame size as the window in order in which the transmission events haveoccurred as shown in FIG. 12. Since the above extracted MAC frames areto be first (re)transmitted, the state of the subsidiary queue 122 inFIG. 12 is referred to as window W1 of FIG. 11. Subsequently, the numberof windows is increased as window W2, window W3 . . . every timetransmission is carried out. In the main queue 121, even in the casewhere a small number of MAC frames is targeted for a series ofretransmission sequences such that a window size is not met, thesubsidiary queue 122 may be configured. Serial sequence numbers SEQ1 toSEQ8 are assigned to the MAC frames extracted in the subsidiary queue122. In addition, data lengths LEN1 to LEN8 of these MAC frames arestored. Further, “N” indicating that a transmission check has notcompleted is set as an initial state of transmission check of each MACframe.

At this time, when the MAC frame to be retransmitted has not beenextracted in the subsidiary queue 122, there is no need for continuingretransmission to at least that communication apparatus (STA1), andthus, a series of the retransmission control processes are terminated(step S2).

Next, even in the case where there exists an undelivered MAC frame, theMAC frame exceeding the retransmission limit, a series of sequences forretransmission to the communication apparatus are canceled (step S3). Atthis time, the undelivered MAC frame in the subsidiary queue 122 isdiscarded (step S9). Here, in the case where an undelivered MAC frameremains in the main queue, such a MAC frame is retransmitted inaccordance with a series of the next retransmission sequences. Thenumber of retransmissions defined as a limit is not limited to aspecific number as described previously, the defined limit may beproperly selected according to a communication party or a communicationmedium state.

Next, the MAC frames are taken out in order from the beginning of thesubsidiary queue 122 to construct a MAC super-frame header and a MACsuper-frame payload (step S4). Then, such a MAC super-frame istransmitted to a destined communication apparatus (STA1 in this case)(step S5). In this manner, the destined communication apparatus receivesthe MAC super-frame and transmits a partial ACK to the MAC super-frame.The transmitting communication apparatus receives this partial ACK fromthe destined communication apparatus (step S6).

Next, in step S7, it is checked whether or not each of the MAC frames inthe subsidiary queue 122 has been transmitted, i.e., whether or nottransmission of the MAC frames has been received in the destinedcommunication apparatus, based on the partial ACK bit map 91 in thepartial ACK frame. Based on the check result, a transmission check statein the subsidiary queue 122 is updated. At this time, the bits of thebit map 91 and the sequence number corresponding to the position in thesubsidiary queue 122 are stored so that their alignments correspond toeach other, and are configured so that their mutual correspondence canbe easily identified. In the example shown in FIG. 1, only the MACframes of SEQ3 and SEQ5 are still set to “N”, which indicates that notransmission has been checked, i.e., which indicates that the frameshave not been transmitted correctly. The Mac frames other than those ofSEQ3 and SEQ5 are set to “Y”, which indicates that a transmission hasbeen checked (RX1). In this manner, transmission check information oneach of the MAC frames indicated in the partial ACK bit map 91 includedin the partial ACK is associated with a MAC frame position of thesubsidiary queue 122 which corresponds to the transmitted MACsuper-frame payload, whereby the transmission check information can beeasily determined.

In step S8, the lowest sequence number of an undelivered frame (forexample, SEQ3 in RX1) is determined as a start point of window. Thisstart point corresponds to a start point of window W2 in transmission(TX2) for a second retransmission. By moving the start point, it becomespossible to discard MAC frames before a sequence number (SEQ3 in TX1)without a first transmission check from the lowest sequence number (SEQ1in TX1) in the subsidiary queue 122. In comparison with window W1, aspace for two window MAC frames is provided. In addition, it becomespossible to easily determine an excess of the retransmission limit inthe previous step S3 by grasping a position of the start point and theend point of this window. For example, if the start point of the windowafter retransmitted by the retransmission limit does not exceed SEQ8assigned to the last MAC frame (i.e. the end point) of window W1, it ispossible to determine that at least one undelivered MAC frame exceedsthe retransmission limit.

When the start point of the window is newly set in step S8, the currentstep reverts to step S1 again in which two MAC frames having the samereceiver address STA1 are sequentially added to the tail of thesubsidiary queue 122 from the main queue 121, and new sequence numbersSEQ9, SEQ19 are assigned. At this time, data lengths LEN9 and LEN10 ofthe added two Mac frames are stored, and a transmission check state isset to “N”. The subsidiary queue 122 is updated in this manner.

That is, in step S1, referring to the subsidiary queue 122 updated instep S8, the MAC frames whose transmission check state is set to “N”follows the stored data length LEN, and 0 is set for the MAC frameswhose transmission check state is set to “Y”. Then, in accordance withstep S4, the MAC super-frame header and the MAC frames whosetransmission check state is set to “N” are selectively taken out inorder from the beginning of the subsidiary queue 122 on the basis of theinformation of the subsidiary queue 122. Then, a MAC super-frame payloadis constructed, and a MAC super-frame to be retransmitted next iscompleted.

Then, in step S5, second transmission (TX2) is executed, and then, theabove-described operation is repeated (TX3 or subsequent).

A beacon has a higher priority of transmission than an ordinary dataframe, and thus, there is a possibility that an interrupt occurs withtransmission of a series of MAC frames as described above. Whendiscontinuity occurs with the sequence numbers in such a case, a seriesof the past retransmission sequences are terminated before suchdiscontinuity occurs, whereby another series of retransmission sequencesmay be started.

On the other hand, FIG. 14 is a view showing a subsidiary queue for usein the receiving communication apparatus, and FIG. 15 is a flowchartshowing operating procedures in the receiving communication apparatus.

In step S1, a MAC super-frame is received. A data length of each MACframe is obtained from a MAC super-frame header and a sequence number isobtained from a MAC header of each MAC frame. Even if an error occurswith any MAC frame in the MAC super-frame, the values of the sequencenumbers are sequentially assigned including MPDUs with zero length.Thus, the sequence numbers of all the MAC frames in the MAC super-framecan be obtained based on the sequence numbers of other MAC frames whichhas been received successfully. Further, a transmission source address(a transmitter address), i.e., a MAC address (STA0 in this case) of thetransmitting communication apparatus is also stored.

In an example of FIG. 11, all the MAC frames other than those of SEQ3and SEQ5 have been normally received, and thus, a receiving state isstored as is (step S2). That is, the receiving states of SEQ3 and SEQ5is set to “N”, and other MAC frames are set Next, the partial ACK bitmap 91 is constructed so as to reflect this receiving state (step S3),and a partial ACK is transmitted to the transmission communicationapparatus (step S4).

As shown in FIG. 14, a processing cost associated with ACK generationcan be reduced by constructing the partial ACK bit map 91 whichcorresponds to an arrangement of MAC frames included in the received MACsuper-frame payload.

Then, the MAC frames from the lowest sequence number (SEQ1 in this case)to a sequence number immediately preceding a first receiving state “N”(SEQ3 in this case) are taken out from the subsidiary queue 131, andthese frames are passed to the upper layer processing step (step S5).

Next, it is determined whether or not all the MAC frames in thesubsidiary queue 131 have been successfully received (step S6). When thereceiving state of all the MAC frames in the subsidiary queue 131 is setto “Y”, all of these received MAC frames are taken out from thesubsidiary queue 131, and the subsidiary queue is emptied. Therefore,this subsidiary queue 131 assigned to STA0 is released and terminated(step S7). On the other hand, in the case where any MAC frame in thesubsidiary queue 131 has not been received, processing reverts to stepS1. In second receiving (RX2), SEQ3 to SEQ9 are taken out, and passed tothe upper layer processing step. Subsequently, the processing of stepsS1 to S6 is repeated with respect to receiving third to fifth MACsuper-frames.

Even if any MAC frame in the subsidiary queue 131 has not been received,if a state in which no MAC super-frame is received from the transmittingcommunication apparatus STA0 continues for a predetermined period oftime, all the MAC frames retained in the subsidiary queue 131 are passedto the upper layer processing step such as link layer processing. Inaddition, in the case where the sequence number of the first MAC framein the MAC super-frame from the transmitting communication apparatusSTA0 is greater than that of the MAC frame waiting for retransmission inthe receiving state “N”, all the MAC frames in the subsidiary queue 131are passed to the high-order processing step, and a new subsidiary queueis generated for a new MAC super-frame. In these cases, a loss of a MACframe occurs.

When the receiving communication apparatus constructs a partial ACK bitmap, only a receiving state of MAC frames included in the immediatelypreceding MAC super-frame may be indicated without referring to ahistory of the past receiving states. Because a partial ACK has to beconstructed and sent within a SIFS time constraint and the requirementof retrieving the past history in this time constraint tends to increasecircuit size and complexity, this simplifies implementation of areceiving communication apparatus. In this case, when the transmittingcommunication apparatus has received the partial ACK, the MAC framewhose transmission has been checked is deleted from the subsidiary queueor a mark indicating that transmission has been checked is assigned tothe corresponding MAC frame, whereby the history of the transmissionstate may be stored.

Further, when the receiving communication apparatus returns the partialACK, the information contained in the physical layer may be fed back tothe transmitting communication apparatus in a form such that it isproperly summarized, by using a PHY feedback information (PHY FeedbackInformation) field 92 of FIG. 9. The transmitting communicationapparatus can switch a transmission scheme for the physical layer (suchas modulation scheme, encoding rate, or number of independent streams ofMIMO) based on both of a transmission state in units of MAC framesexpressed by partial ACK bit map 91 and the PHY feedback information 92.For example, in the case where all the MAC frames have been receivedsuccessfully, it is possible to check whether or not a margin of thephysical layer is large. If the margin is large, it is possible tochange a current transmission scheme to a higher data rate transmissionscheme. If an error occurs with several MAC frames, it is possible todetermine whether to reduce a modulation scheme level or encoding rateto save the margin or whether to reduce the number of MIMO independentstreams. By doing this, the information required for controllingcommunication in the physical layer can be transmitted whiletransmission and reception of the MAC frame are carried out.

FOURTH EMBODIMENT

The present embodiment describes a case in which it is permitted that apartial ACK frame in addition to data frames is included as a MAC frameconfiguring a MAC super-frame. Further improvement of a throughput canbe expected by piggybacking a partial ACK in the MAC super-frame.

FIG. 16 shows a frame configuration in the case where a partial ACKframe is permitted as a first MAC frame of the MAC super-frame payload203. In addition, a carrier sense state in this case is shown in FIG.17. Now, a difference from the embodiments described previously will beprimarily described here.

The partial ACK frame of FIG. 16 includes only address 1, namely only anaddress of a receiving communication apparatus, and does not includeaddress 2 to address 4. Address 1 and a value of a duration field areinformation sufficiently required to carry out virtual carrier sensingof a MAC layer.

In the present embodiment, when a transmission privilege utilizing acommunication medium has been allocated, a sequence can be configuredsuch that a plurality of MAC super-frames and the last partial ACK aresequentially transmitted and received at a SIFS interval (namely,without new procedures for allocating or contending for a transmissionprivilege).

FIG. 17 shows an example of a carrier sense state for defining a valueof a duration field in the communication apparatus according to thepresent embodiment. FIG. 17 shows an example in which a series ofcommunication processes terminate when three frames are exchanged. Asequence may be further continued. A maximum TXOP (TransmissionOpportunities) of FIG. 17 indicates a maximum time permitted for onesequence. The TXOP is notified to each communication apparatus as avalue common to all the communication apparatuses by means of beacon,for example. Alternatively, it is considered that a communicationapparatus (e.g. an access point) for concentrically managing a useprivilege of a communication medium dynamically assigns a transmissionprivilege having individual TXOP values for individual communicationapparatuses.

When a value of a duration which corresponds to a sum of the SIFS andpartial ACK frame transmission time is set such that the communicationapparatus occupies a communication medium during transmission, it mustbe considered that it is not always evident as to whether a partial ACKincluded in a response is transmitted by a first type PHY frame or istransmitted by a second type PHY frame. In general, in the case where nodata frame is to be transmitted by a counterpart communicationapparatus, or alternatively, in the case where the data frame is notincluded in the TXOP, although an attempt is made to include the dataframe, transmission is carried out in the first type PHY frame. In theother case, a partial ACK is transmitted in accordance with the secondtype PHY frame. Using the first PHY frame reduces a transmission time ofa frame including a partial ACK more significantly because the PHYheader of the second type PHY frame is longer than that of the firsttype PHY frame; a data length of the partial ACK itself is shorter; anda time interval required for transmitting this partial ACK does notdepend on a transmission rate so much. When a value of the longer headeris set as a duration value, a communication medium is unnecessarilyoccupied, and a wasteful time which is not utilized in anothercommunication process is likely to occur. Thus, a value of the shorterheader is set as a duration value.

In FIG. 17, a value obtained when it is assumed that a partial ACK istransmitted in accordance with the first type PHY frame is set asduration values of MAC frame 1 and MAC frame 2. In actuality, a case inwhich a partial ACK (corresponding to MAC frame 3) has been transmittedin accordance with the second type frame is indicated. Although duration1 is indicated as a value which terminates before completion of partialACK transmission, the communication apparatus 3 and communicationapparatus 4 each detect a PHY busy state in a duration of NAV set inaccordance with duration 1. While the PHY busy state of thecommunication apparatus 3 continues, NAV of the communication apparatus3 is updated by a value of duration 2 included in the partial ACK (MACframe 3) and MAC frame 4. Thus, the state of carrier sensing of thecommunication apparatus 3 does not cause a problem for a virtual mediumoccupation duration of the communication. With respect to thecommunication apparatus 4 as well, after the receiving of the secondtype PHY frame including the partial ACK has completed, the EIFSduration is restarted. Therefore, no problem occurs with the carriersense state of the communication apparatus 4. Accordingly, even if aduration value is calculated assuming that a partial ACK is transmittedin the first type PHY frame, it is found that no problem occurs withrespective communication apparatuses on the communication. Therefore,with such a configuration according to the present embodiment, thepartial ACK can be efficiently transmitted while one communicationapparatus coexists with another communication apparatus.

In the case where a partial ACK included in the MAC super-frame has notbeen correctly received, this partial ACK may not be retransmitted. Inthis case, recovery may be carried out similarly in the case where apartial ACK without aggregation has been lost. Namely, after it isdetected that a partial ACK has not been successfully received, a MACsuper-frame identical to that transmitted immediately before includingthat partial ACK is retransmitted.

FIFTH EMBODIMENT

The present embodiment relates to a case of aggregating (integrating) aplurality of MPDUs generated when one MSDU has been fragmented.

FIG. 18 shows an example of a MAC super-frame header in accordance withthe present embodiment. In addition to each MAC frame length (MAC Framelength), a fragment number of each MAC frame is included. The handlingof a fragment number will be described below.

It is presumed that MPDU configuring one MSDU does not encompass anotherMAC super-frame. Sequence numbers are assigned so as to be sequentialvalues relevant to MSDU. Namely, the MPDU generated from the same MSDUhas the same sequence number. A fragment number is a value representinga relative position of the MPDU in MSDU, and are generally assigned as acontinuous value beginning with 0. Finally, the sequence number andfragment number, and the relative position of each MAC frame in a seriesof transmission/retransmission processes for MAC super-frames aredecided at the time of transmission. Accordingly, the transmittingcommunication apparatus can specify a corresponding MAC frame by usingonly partial ACK bit map information, and can make retransmissioncontrol by simple expansion in the scheme described previously.

Alternatively, retransmission control according to the presentembodiment can be functioned similarly even by indicating the first andlast MPDU of MSDU (either of them may be implicitly indicated) withoutexplicitly indicating a fragment number in a MAC super-frame header.

SIXTH EMBODIMENT

At a MAC super-frame header according to the present embodiment, the MACsuper-frame header itself has the same format as the MPDU. A receivingcommunication apparatus can carry out branching of processing of anordinary MAC frame and a MAC super-frame by only processing of a MAClayer without receiving information from a physical layer.

FIG. 19 shows an example of a MAC super-frame header 1900 which has thesame format as the MPDU. For example, a value indicating a MACsuper-frame header is newly defined and assigned in a Type/Sub-typeregion included in a frame control field. The MAC layer of the receivingcommunication apparatus determines whether to carry out processing ofthe MAC super-frame subsequently or whether to carry out processing anordinary MAC frame in accordance with the value. The value of theduration 504 is set in conformance with a method for calculating a valueof another MAC frame included in the MAC super-frame. The value of field505 of address 1 (Receiver Address) is set to be identical to address 1of another MAC frame included in the MAC super-frame. In this manner, anaddress for specifying the receiving communication apparatus is set infield 505 of address 1.

The MAC super-frame header 1900 is neither fragmented nor retransmitted,and thus, the value of sequence control field 508 does not have meaningin particular. Therefore, it is more preferable that type of the MACsuper-frame is assigned as a control frame because this sequence controlfield 508 is emitted.

When type of defined as Management or Data, it is necessary to have thesequence control field 508. This value need to be handled so as toobtain coincidence with retransmission control of the embodimentaccording to the present invention. In the existing communication, it isassumed that the sequence number of the MAC frame targeted forretransmission takes a continuous value in a series of retransmissioncontrols for the MAC super-frame, for example. Thus, in the case where adiscontinuous value is set for a sequence number, a series ofretransmission controls for the MAC super-frame are temporarilyterminated, making it necessary to start retransmission control usinganother sequence. Thus, it is necessary to ensure that sequence numberdiscontinuity does not occur or to continue a series of retransmissioncontrols even if the sequence number becomes discontinuous. As oneexample for solving this problem, there is a method for, when windowcontrol is made during retransmission as shown in another embodiment ofthe present embodiment, it is possible for a transmission communicationapparatus to find the maximum sequence number which can be assigned tothe MAC frame targeted for retransmission in a series of retransmissioncontrols in advance. Thus, sequentially allocating the sequence numbersof a value, which exceeds the maximum value of sequence number, to MACsuper-frame MPDSs solves the problem. Further, it is necessary to assigna continuous value to this value including a MAC frame targeted forretransmission. However, there can be provided a method for, whenretransmission control is made, ignoring the sequence number of the MACframe targeted for retransmission, thereby controlling retransmission soas to permit discontinuity. A retransmission control method which mainlydepends on relative positions of MAC frames in a sequence of MACsuper-frames and not entirely relies on sequence numbers of MAC framesis an example of this method.

A length of each MAC frame included in the MAC super-frame is set at aportion 1901 corresponding to a payload shown in FIG. 19. As describedin another embodiment of the present invention, a fragment number forcoping with fragmentation may be included in the payload 1901.

In addition, FCS 502 corresponds to the HCS 205 shown in FIG. 2. In thecase of the present embodiment as well, using the FCS 502 may be handledin the same manner as in normal MPDU. For example, a CRC valuecalculated relevant to the whole MAC super-frame header is set in theFCS 502. In the case where it is recognized that the MC super-frameheader 1900 is destroyed by the FCS 502 associated with the MACsuper-frame header 1900, this recognition is handled in the same manneras in the case where an error has been detected by the HCS 205. Thereceiving communication apparatus having detected this error discardsthe whole MAC super-frame.

SEVENTH EMBODIMENT

In the present embodiment, the MAC super-frame header which can behandled in the same manner as a partial ACK and the MAC frame shown inanother embodiment of the present invention is stored in the same MACsuper-frame.

FIG. 20 shows an example of a format of a MAC super-frame 200 inaccordance with the present embodiment. Here, a partial ACK frame isfirst arranged at the head of the MAC super-frame payload 203, and then,a MAC frame of the MAC super-frame header is set in order. Essentialinformation included in a MAC super-frame header 2001 corresponds to alength of each MAC frame required for the receiving side to recognize aboundary of respective MAC frame in the MAC super-frame payload 203. Alength of a partial ACK can be basically set at a fixed length. Thus,even if a partial ACK is placed at the beginning, no problem occurs withprocessing in the receiving communication apparatus. There is a highpossibility that, even if the length of the partial ACK is placed at thebeginning, whereby the preceding ACK can be received without any problemeven if the MAC super-frame header is destroyed. When a partial ACK isreceived without any problem, since a carrier sense state of the MAClayer is correctly set, second required retransmission can be carriedout without a waiting time for error recovery. In this manner, thewaiting time for error recovery can be eliminated, whereby improvementof a communication throughput can be expected.

In contrast, even if a positional relationship of the partial ACK andthe MAC super-frame header 2001 is reversed in the MAC super-framepayload 203, if the MAC super-frame header 2001 is set at a fixedlength, there is a possibility that, even if the preceding MACsuper-frame header 2001 is destroyed, the subsequent existing partialACK can be correctly received. A similar advantageous effect can beattained if carrier sensing and retransmission control are made based onthe partial ACK similarly.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A communication apparatus comprising: a receiving device configuredto receive a physical frame which includes a plurality of medium accesscontrol frames; an acquisition device configured to acquire virtualcarrier sense information from at least one medium access control frameof a plurality of medium access control frames included in the physicalframe received by the receiving device; and a device configured tospecify a duration in which a communication medium is virtually occupiedbased on the virtual carrier sense information acquired by theacquisition device, and configured to wait for transmission of a frameonto the communication medium in the duration.
 2. A communicationapparatus according to claim 1, wherein: the device is configured to seta duration in which the communication medium is virtually occupied, witha start time as a receiving end time point of the last medium accesscontrol frame included in the physical frame received by the receivingdevice, and with an end time as a time point corresponding to an end ofthe duration.
 3. A communication apparatus according to claim 1,wherein: the device is configured to set a duration in which thecommunication medium is virtually occupied, with a start time as areceiving end time point of the physical frame received by the receivingdevice, and with an end time as a time point corresponding to an end ofthe duration.
 4. A communication apparatus according to claim 1,wherein: the device is configured to set a duration in which thecommunication medium is virtually occupied, with a start time as areceiving end time point of any one of the medium access control frameincluded in the physical frame received by the receiving device, andwith an end time as a time point corresponding to an end of the durationcomputed from the virtual carrier sense information included in themedium access control frames.
 5. A communication apparatus according toclaim 1, further comprising: a power saving control device configured,in the case where the physical frame received by the receiving device isa physical frame destined to another communication apparatus, to set thecommunication apparatus at a power saving state in the duration.
 6. Acommunication method comprising: receiving a physical frame having aplurality of medium access control frames; acquiring virtual carriersense information from at least one medium access control frame of aplurality of medium access control frames included in the physical framereceived; and specifying a duration in which a communication medium isvirtually occupied based on the virtual carrier sense informationacquired, and waiting for transmission of a frame onto the communicationmedium in the duration.
 7. A communication method according to claim 6,further comprising: setting a duration in which the communication mediumis virtually occupied, with a start time as a receiving end time pointof the last medium access control frame included in the physical framereceived, and with an end time as a time point corresponding to an endof the duration.
 8. A communication method according to claim 6, furthercomprising: setting a duration in which the communication medium isvirtually occupied, with a start time as a receiving end time point ofthe physical frame received, and with an end time as a time pointcorresponding to an end of the duration.
 9. A communication methodaccording to claim 6, further comprising: setting a duration in whichthe communication medium is virtually occupied, with a start time as areceiving end time point of any one of the medium access control frameincluded in the physical frame received, and with an end time as a timepoint corresponding to an end of the duration computed from the virtualcarrier sense information included in the medium access control frames.10. A communication method according to claim 6, further comprising:setting the communication apparatus at a power saving state in theduration, in the case where the physical frame received is a physicalframe destined to another communication apparatus.